Chapter 8Stoichiometry

What is Stoichiometry?-deals with quantities of materials consumed

and produced in chemical reactionsWhat info is needed for stoichiometry

problems?1. Balanced chemical equation2. Mole ratio- conversion factor that relates

amounts in moles of any 2 substances3. Molar mass- conversion factor that relates

mass of a substance to the amount of moles of that substance

Stoichiometry Examples

Oxygen can be produced by the decomposition of potassium chlorate. In the process potassium chloride is also produced.

1. Write a balanced equation.2KClO3 3O2 + 2KCl

a) If you had 11.3 moles of potassium chlorate, how many moles of oxygen would be produced?

b) How many grams of potassium chlorate would be produced from 9.30 moles of oxygen?

Con.

c) How many moles of potassium chloride will be produced in the reaction if 94.7 g of oxygen are produced?

d) How many grams of oxygen would be produced when 49.89 g of potassium chlorate decomposes?

Using Density with Stoichiometry

What is density?D=mass/volumeExample: In the space shuttles, the CO2 that

the crew exhales is removed from the air by a reaction with canisters of lithium hydroxide. On average, each astronaut exhales about 20.0 moles of CO2 daily. Water and lithium carbonate are produced in this reaction. What volume of water will be produced when this amount of CO2 reacts with excess Lithium hydroxide. ( Hint: the density of water is about 1.00g/ml.)

Con.

Magnesium burns in oxygen to produce magnesium oxide. How much magnesium will burn in presence of 189 ml of oxygen. The density of oxygen is 1.429 g/L.

2 Mg + O2 2MgO

Limiting and Excess Reactants

Limiting Reactant- reactant that is used up first

Excess Reactant- reactant that is not completely used up

How can the limiting reactant be determined?

Set up 2 mole problems. The smaller amount is the limiting reactant.

Limiting/excess example

Carbon monoxide can be combined with hydrogen to produce methanol, CH3OH. Methanol is used as an industrial solvent, as a reactant in synthesis, and as a clean-burning fuel for some racing cars. If you had 152.5 kg CO and 24.50 kg H2, how many kilograms of methanol would be produced?

CO (g) + 2H2(g) CH3OH(l)

Another example

Ammonia,NH3, is used throughout the world as a fertilizer. To manufacture ammonia, nitrogen is combined with hydrogen in a synthesis reaction. If 92.7 kg of nitrogen and 265.8 kg of hydrogen are used, which is the limiting reactant?

Theoretical Yield

- calculated maximum amount of product possible

Actual yield- amount of product actually created

Percent yield= actual yield • 100theoretical yield

Percent Yield Example

Determine the limiting reactant and the percent yield if 14.0 g of nitrogen react with 3.15 g of hydrogen to give an actual yield of 14.5 g of NH3.